1. Field of the Invention
The present invention relates to a broadcasting system, and particularly relates to a receiving apparatus of the broadcasting system.
2. Description of the Prior Art
Digital broadcasting signals can be classified into digital audio broadcasting (DAB) and digital video broadcasting (DVB). DAB has various standards such as European Standard Eureka-147 (which Taiwan follows), USA IBOC and France DRM, and DVB has DVB-T and DVB-H. Furthermore, each of the standards has different bandwidths; for example, DVB-T has a bandwidth of 6, 7 or 8 MHz, and DAB has a bandwidth of 1.536 MHz. Additionally, each nation also has its own standards; for example, Korea has T-DMB (Terrestrial Digital Multimedia Broadcasting). Therefore, a receiving system requires special design to receive these signals complying with different standards.
In order to integrate various standards into a single receiver, one method is to utilize a tuner, which includes a plurality of SAW filters with different bandwidths, but the cost will increase due to this method. FIG. 1 illustrates another conventional receiving system 100 for the DVB-T and DAB standards. Please refer to FIG. 1, the tuner 101 utilizes one SAW filter as a channel selecting filter to select DVB-T channels, a digital low-pass filter 107 can be utilized to select DAB channels for DAB standard with narrower signal bandwidths. The receiving system 100 includes a tuner 101, an ADC 103, a down converter 105, a digital low-pass filter 107, a FFT (Fast Fourier Transform) circuit 109, a post-processing circuit 111 and a synchronization circuit 113, wherein the synchronization circuit 113 is used for providing synchronization information to the FFT circuit 109. Since the detailed structures and operation of the conventional receiving system 100 are well known by persons skilled in the art, they are omitted for brevity. It should be noted that the output signal SIF of the tuner 101 always includes a plurality of DAB channels (ex: right and left adjacent channel signals (ACS)) when the receiving system 100 is set to receive a DAB signal. FIG. 2 illustrates the output signal of the tuner 101 in FIG. 1. Due to the effect of the large ACS interference, the ADC 103 and the digital circuit (ex: low-pass filter 107) may need more bit-number (resolution). At the same time, the output signal of the tuner 101 includes at least one of ACS signal with a large strength, and therefore the effect and sensitivity of the whole system will decrease. Thus, a new invention is needed to solve above-mentioned problems.